1. Field of the Invention
The present invention relates generally to a fuel supply control system for an internal combustion engine for an automotive vehicle. More specifically, the invention relates to a fuel supply control system, particularly applicable for the internal combustion engine with a supercharger, such as a turbocharger.
2. Description of the Background Art
In a turbocharged internal combustion engine, exhaust temperature can become excessively high at high load condition to damage exhaust valve, exhaust manifold, turbine of a turbocharger and so forth. Therefore, in the prior art, a target air/fuel ratio is set at excessively rich in a predetermined load range, such as high load range at 6000 r.p.m. or higher, in order to cool an engine combustion chamber with fuel to lower the exhaust temperature. Also, even in the steady state, the target air/fuel ratio is set so that the exhaust temperature can be maintained lower than or equal to a predetermined value.
However, since there is large heat mass in the exhaust system, the problem of rising of the exhaust temperature during steady state driving can be ignored during engine transition state, such as engine accelerating state, to high load range. In contrast, over-rich air/fuel ratio during the transition state may cause degradation of fuel economy and create associated problem of exhaust gas emission, i.e. increasing of CO emission.